In Python 3, all of these were "consolidated" under urllib(.request,
.parse, .errors) which is inconvenient.
Since we already have hard dependencies on requests and
werkzeug(.urls, which is a backport of Python 3's unicode-aware
urllib.parse) migrate *everything* to that.
A sticking point is urllib2.URLError, those were (mostly) replaced by
the slightly more general IOError which URLError extends.
Xavier Morel
01e3514147